Post Traumatic Stress Disorder (PTSD) can occur when a disturbing event is experienced as being so traumatic that it overwhelms the person's ability to deal with it mentally. Such events typically are rapes, assaults, road traffic accidents, operative procedures, sexual abuse, natural disasters, but can also be a wide range of disturbing events.

Whether the traumatic event results in the development of PTSD will be affected by factors such as the persons previous life experiences, the nature of the event itself, and the kind of post trauma support available to the person.

When ordinary anxiety arising events occur, we deal with them mentally by talking about them, emoting about them and going through a process often called "working through". If PTSD occurs however, this usually helpful response of talking about and emoting about, a disturbing event, no longer works, and in fact can actually result in the person feelings worse. For this reason people with PTSD will usually try and block out memories of what happened to them. This blocking out or "avoidance" causes memories of the trauma to be triggered by events that will remind the person of what happened to them. For example, the noise of a car accelerating, for someone who has been in a road traffic accident. These triggers will result in an overwhelming feeling of threat and panic.

Another key element is that even though PTSD sufferers know that the traumatic event happened in the past, it becomes impossible to think about it without feeling the same emotions and sensations that occurred at the time the original experience, and it can sometimes feel as if the trauma is happening again now – a phenomenon we call "flashbacks". People also frequently develop negative ways of thinking about themselves in relation to the trauma, eg. "I caused it" or "I’m a bad person". These beliefs can start to influence how people feel about themselves in other situations as well.

These symptoms cause the person to avoid any situation that reminds them of what happened in the original trauma and also causes other difficulties such as poor sleep, poor concentration and a constant feeling of threat.

EMDR is the most rapid and effective way we know to desensitise the images and feelings associated with the original trauma, and it can help in guiding the person to think differently about themselves in relation to the trauma.